1. Field of the Invention
The present invention relates to a system for processing 4-color data, and more particularly to an organic electro-luminescent display (OELD) device and a method for processing 4-color gray-scale data to improve luminance and color sensitivity of displayed colors.
2. Description of the Related Art
In general, liquid crystal display (LCD) devices improve luminance by employing 4-color pixels each having white color (W) in addition to red color (R), green color (G) and blue color (B). Such LCD devices improve the luminance of white color or an achromatic color obtained from a mixture of colors. However, in case of colors having high color purity such as primary colors, luminance of those colors is decreased and color sensitivity is also deteriorated when employing the method of mixing colors.
FIG. 1 is a graph for describing a conventional 4-color display. Referring to FIG. 1, displayable colors in RG system are within the rectangle area defined by points 0, R, RG and G. In the RG system, two-color (i.e., red and green) data is processed and colors are displayed by two-color pixels each having red and green. An RGY system may be defined by means of the RG system. The RGY system has a red pixel, a green pixel and a yellow pixel that is an optical mix of the red pixel and the green pixel. The optical mix increases the luminance of the RG system.
Assuming that the maximum luminance of the optical mix of the red and green pixels is substantially the same as the maximum luminance of the yellow pixel, the maximum luminance of an optical mix of the red, green and yellow pixels is two times brighter than the maximum luminance of the optical mix of the red and green pixels. Therefore, an optical mix of color pixels increases luminance.
However, when a primary color is displayed, it is difficult or unable to increase luminance of the primary color pixel. For example, when primary red color is displayed by a red pixel, luminance of the red pixel is not increased without a yellow pixel. Therefore, displayable colors in RGY system are within the hexagonal area defined by points 0, R, R′G, R′G′, RG′ and G.
As a result, a color of a first original gray-scale data (I) may be displayed by using a first compensated gray-scale data (I′) that are extended twice, but a color of a second original gray-scale data (II) may be displayed by using a second compensated gray-scale data (II′) that are extended less than twice. This is because while the first original gray-scale data (I) is within the rectangle area defined by points 0, R′G, R′G′ and RG′, the second original gray-scale data (II) is out of the rectangle area.
Luminance of a mixed color existing within the rectangle area defined by points 0, R1, RG and G1 may be increased twice. However, luminance of a mixed color existing within the triangular area defined by points 0, R and R1 or the triangular area defined by points 0, G and G1 may not be increased twice. Also, since the size of a pixel in the RGY system decreases compared with that in RG system, luminance of RGY system decreases as well.
For the same reasons for the RG and RGY systems, luminance in RGB or RGBW system also decreases. Especially, there is no or little advantage of improving luminance in case of displaying primary colors, and luminance may be decreased because of a decrease in the pixel size.
Therefore, a need exists for a multiple color data processing system which improves optical efficiency while preventing decrease or deterioration of luminance and color sensitivity.